1. Field of the Invention
The present invention relates to a single use, self-annulling syringe that is rendered inoperative after a single injection without requiring any deliberate action on the part of the user. Passive inactivation is desirable to eliminate syringe/needle reuse which has been identified as a source for spreading blood-transmitted infectious diseases.
2. Description of the Prior Art
In both the United States and particularly in third world countries, multiple use of unsterile needles and unsterile syringes can transmit infectious agents including hepatitis viruses and LAV/HTLV-III, a virus which causes the acquired immunodeficiency syndrome (AIDS).
The prior art teaches various methods and apparatuses for breaking off and storing the needle portion of the syringe so that the syringe cannot be reused. The following U.S. patents are illustrative of this technique: U.S. Pat. Nos. 3,306,291; 3,796,359; 3,893,608; 4,121,588; 4,220,151; 4,266,544; 4,270,536; and 4,333,457. However, for these syringes to be single use, action (e.g., breaking off the needle tip) must be taken by the medical staff. Public health researchers have found that medical staff, particularly in third world countries, are not taking the action necessary to render these syringes inoperative. Therefore, passive inactivation of the syringe is desirable--that is, a syringe that is rendered inoperable without requiring any deliberate action, (e.g., breaking the needle) on the part of the user or the medical staff.
The prior art also teaches various syringes having a means for destroying the syringe cylinder during the injection stroke. U.S. Pat. Nos. 3,667,657; 3,951,146; 3,998,224 and 4,391,273 issued to Marcello Chiquiar-Arias teach the use of a syringe piston that contains a sharpened portion which destroys the syringe cylinder during downstroke. In U.S. Pat. No. 3,667,657 a knife edge attached to the piston cuts through the syringe cylinder. In U.S. Pat. No. 3,951,146 the knife edge is mounted with a spring mechanism allowing the piston to initially draw fluid into the syringe with the knife edge remaining in a recessed position. U.S. Pat. Nos. 3,998,224 and 4,391,273 teach a punching element mounted on the bottom of the piston for piercing the syringe cylinder when the piston is pressed in a downward position. Using a similar technique in U.S. Pat. No. 4,062,287, the forward edge of the syringe cylinder wall and the lower end of the plunger wall have mating surfaces. These surfaces mate when the plunger is pressed into its most downward position. Once the surfaces have mated, motion of the plunger will cause the end walls to break away from the barrel.
Certain other syringes appearing in the prior art utilize a locking means to prevent multiple use. U.S. Pat. No. 3,478,937, issued to I. Solowey, teaches two embodiments of a mechanical locking mechanism. In the first embodiment, a flexible disk flexes to pass through the central opening of the syringe during the downstroke of the plunger. Once through the central opening, the flexible disk is shaped so that it can no longer pass through the central opening during the upstroke of the plunger. Therefore, the syringe can only be used once. In the second embodiment, two pivotal pawls replace the flexible disk. Once the pawls have passed through the central opening they extend outward because of a spring mechanism. Once the pawls are extended, the plunger is inoperative. U.S. Pat. No. 4,233,975, issued to Arthur Yernan, also teaches two embodiments for freezing the motion of the plunger after injection. In the first embodiment, downward motion of the plunger causes a plug element to be pushed forward and locked into a female portion. Once the plug element is so engaged, fluid flow into the hypodermic needle is blocked. In the second embodiment, the piston itself contains a flexible portion that will fill a recess, thereby locking the piston in a downward position. Any attempt to pull the piston from its downward position will cause separation of the piston rod from the piston. Other mechanical locking means are taught in U.S. Pat. Nos. 4,367,738; 4,391,272; 4,493,703; and 4,252,118.
U.S. Pat. No. 3,874,383, issued to John Glowacki, uses a plastic insert made of a heat deformable material that is placed within the lower portion of the syringe cylinder. If any attempt is made to sterilize or autoclave the liner it will heat, distort and shrivel up. In the embodiment shown in FIGS. 1-3 of Glowacki, this would render the syringe inoperative and in the embodiment shown in FIGS. 4-5 of Glowacki would remove the Luer lock flanges so that a second syringe needle cannot be fitted into the hub. However, the Glowacki reference does not prevent reuse of an unsterilized syringe--it merely prevents attempts to sterilize a syringe for a possible second use.